There has been great interest in fabricating cold cathodes using wide-band-gap semiconductors. Such material has been used as coatings on metallic tips, as tip materials, and as thin-film cold cathodes. Materials of current interest include among others diamond, nitrides, disordered carbon forms, and others.
Electron emission is achievable in many ways from a variety of materials and several mechanisms have been proposed to explain the phenomenon. For example, a disordered tetrahedral carbon thin-film device using a diode configuration has been successfully demonstrated in applications for such purposes. (To this purpose see the article by B. L. Weiss, A. Badzian, L. Pilione, T. Badzian, and W. Drawl, Appl. Phys. Lett. 71, 794 (1997).) This material seems to satisfy the provide the following qualities:
(i) electronic structure characteristics of wide-band-gap semiconductors; PA1 (ii) high dielectric breakdown; PA1 (iii) n-type electrical conductivity; PA1 (iv) favorable emission surface properties, including negative electron affinity and/or emission enhancement by adsorbed specific atoms; and PA1 (v) durability under a high electrical field, including longevity in thousands of hours.
In general, diamond material fulfills these conditions as is demonstrated in the extensive electron emission art. Examples include: U.S. Pat. No. 3,947,716, issued on Mar. 30, 1976, to Fraser, Jr. et al.; U.S. Pat. No. 3,970,887, issued on Jul. 20, 1976, to Smith et al.; U.S. Pat. No. 4,307,507, issued on Dec. 29, 1981, to Gray et al.; U.S. Pat. No. 4,685,996, issued on Aug. 11, 1987, to Busta et al.; U.S. Pat. No. 4,955,636, issued on Aug. 8, 1989, to Busta et al.; U.S. Pat. No. 4,964,946, issued on Oct. 23, 1990, to Gray et al.; and U.S. Pat. No. 5,703,435, issued Dec. 30, 1997.
According to some of the teachings of the art, chemical vapor deposition (CVD) methods were used in the fabrication of emission devices because of their versatility.
Of these requirements, the most difficult to achieve is the n-type diamond, preferably as a shallow donor material. However, n-type diamond was reported as a result of P (phosphorous) doping of (111) homoepitaxial thin films. In this investigation, Hall measurements were taken and an activation energy of 0.46 eV was calculated. (See S. Koizumi, M. Kamo, Y. Sato, H. Ozaki, and T. Inuzuka, Appl. Phys. Lett. 71 (1997) at 1065.)
While providing arguable improvements in the art, the prior art fails to provide a practical method of providing a diamond suitable for providing electron field emission. Such a method remains wanting.